Sulaymaniyah, Iraq — Iraq's Kurdish forces said Monday they have seized a strategic dam from the self-declared Islamic State (IS) after heavy US air strikes, a victory for the Kurdish peshmerga that may also suggest mission creep for Washington.

“The peshmerga have complete control over the Mosul Dam,” Kawa Edo Alxetare, a member of the Kurdish Democratic Party, told The Monitor. An Iraqi military spokesman told The Associated Press that Iraqi forces also took part in the offensive and that the southern side of the dam complex was still contested.

The hydroelectric dam was one of the jewels in the vast territory captured in recent months by IS fighters. The threat the radical Sunni group poses to strategic oil installations, religious minorities, and the stability of Iraq combined to spur the US and its allies back into Iraq.

“The dam’s capture put a crown on the Islamic State conquests. Losing the dam tarnishes the momentum which they used to amplify victory and claim God was on their side,” says Michael Rubin, a former Pentagon official now at the American Enterprise Institute. “The White House understands Iraq is too important to fail."

Bombing experts were working around-the-clock to dismantle explosives left behind by IS in the residential complex of the hydroelectric dam, Iraq's largest, which supplies electricity to the national grid.

US air strikes paved the way for peshmerga forces to assert control in many of the villages surrounding the dam, including the Arab town of Wana. The peshmerga also took the Christian town Tel Iqof, a Yazidi hamlet, and the villages of Baqufa and Batnaya. That advance brought the peshmerga within 12 miles of Nineveh, on the eastern bank of the Tigris River, according to Mr. Alxetare, who spoke from a frontline position near the dam.

“The air strikes destroyed more than 50 vehicles and killed many of them [IS fighters],” says Alxetare, adding that another 20 IS combatants had been taken as prisoners by peshmerga forces. Five peshmerga, he said, were wounded by an improvised explosive device (IED) in Babera as they made their way to liberate the dam.

The US military for its part said fighter jets and drones had attacked IS fighters for a second day on Sunday, destroying three armed vehicles, a vehicle mounted with an anti-aircraft artillery gun, a checkpoint, and an IED emplacement. At least 14 vehicles were destroyed in air strikes the pervious day.

A limited rollback?

Mr. Rubin says the unanswered question for President Barack Obama is whether it’s enough to roll back IS a few miles, effectively allowing them to keep other territory seized since June – or whether its unacceptable for the Al-Qaeda offshoot to rule any territory in Iraq.

“Whether or not the goal is to eliminate the Islamic State or simply stop it, is a decision which the White House has yet to make or explain,” he said.

IS has strategically focused on oil and water resources in Iraq and Syria. It controls two refineries and up to seven oil fields in northern Iraq.

Kurdish control over Mosul dam should open up vital water supply lines to the beleaguered Iraqi army, which had struggled to confront IS fighters on the ground. Today's apparent victory also offers the peshmerga a chance to redeem their reputation as effective fighters in the eyes of the West.

“It is extremely important that they [peshmerga] can show the world that they are able to control the dam and push out ISIS from areas where they have de facto or complete control,” says Michael Stephen, deputy director at the Royal United Services Institute in Qatar.